The head of the Federal Bureau of Investigation - the FBI - said Monday that the main threat of global terrorism is coming from the tribal areas of Pakistan and Afghanistan.

FBI Director Robert Mueller says another threat could come from militants recruited on U.S. soil. He says, the terror attacks in Mumbai, India last November have raised concerns about whether a similar attack could happen elsewhere.

Militants armed with rifles and grenades struck 10 sites, including a train station, Jewish community center and two luxury hotels. Almost 200 people were killed and more than 300 wounded.

"This type of attack reminds us that terrorists with large agendas, and little money can use rudimentary weapons to maximize their impact," Mueller said.

The FBI director spoke at the Council on Foreign Relations, a foreign policy research group in Washington D.C.

He said the tribal areas of Afghanistan and Pakistan pose the greatest threat of terror attacks.

But he said there is growing concern about people around the world who support al-Qaida. He said the U.S. must be concerned about other possible threats, including from people who don't need a visa to enter the United States.

"We must also focus on less well-known terrorist groups, as well as homegrown terrorists," he said. "And we must consider extremists from visa-waiver countries, who are merely an e-ticket [airline ticket bought on internet] away from the United States."

The FBI director said there is concern about terrorists being recruited on American soil. He said a man from the Midwestern city of Minneapolis was recruited for terrorist acts. Minneapolis has the largest Somali population in the United States. Somalia has been engulfed in civil conflict for years.

"A man from Minneapolis became what we believe to be the first U.S. citizen to carry out a terrorist suicide bombing," he said. "The attack occurred last October in southern Somalia, but it appears that this individual was radicalized in his hometown in Minnesota."

Mueller said men from other communities in the United States have been recruited to fight in Afghanistan, Iraq, and Yemen.

He said the FBI is trying to counter that through increased contact with, and better understanding of Muslim communities in the United States.